Pyrrolidine-2-thione derivatives as herbicides

ABSTRACT

Pyrrolidine-2-thione derivatives of the formula (I) ##STR1## wherein the variables are as defined in the specification are active as herbicides.

This application is a 371 of PCT/GB95/01223 filed May 26 1995.

This invention relates to chemical compounds useful as herbicides, toprocesses for preparing them, and to herbicidal compositions andprocesses utilising them.

Herbicidal compounds based upon carbonyl substituted nitrogen containingheterocyclic rings are known for example from British Patent No. 1345159and DE OS 2212558.

The applicants have found a group of compounds which have a particularsubstituent pattern and which are active as herbicides.

According to the present invention there is provided a compound offormula (I):

Wherein R¹ and R² are each independently hydrogen, optionallysubstituted lower hydrocarbyl, or optionally substituted heteroaryl, orR¹ and R² together with the nitrogen atom to which they are attached,form a heterocyclic ring; R³, R⁴, R⁵ and R⁶ are independently H or C₁₋₄alkyl; Z represents halogen, optionally substituted lower hydrocarbyl,optionally substituted lower hydrocarbyloxy, optionally substitutedlower hydrocarbylthio, hydrocarbylsulphinyl, or hydrocarbylsulphonyl,cyano, nitro, CHO, NHOH, ONR^(7') R^(7"), SF₅, CO(optionally substitutedlower hydrocarbyl), acylamino, COOR⁷, SO₂ NR⁸ R⁹, CONR¹⁰ R¹¹, OR¹² orNR¹³ R¹⁴ where R⁷, R^(7'), R^(7"), R⁸, R⁹, R¹⁰ and R¹¹ are independentlyH or lower hydrocarbyl; R¹² is hydrogen, SO₂ lower hydrocarbyl or COR¹⁵; R¹³ and R¹⁴ are independently lower hydrocarbyl, lower hydrocarbyloxyor a group R¹² ; R¹⁵ is OR¹⁶, NR¹⁷ R¹⁸, hydrogen or lower hydrocarbyl;R¹⁶ is lower hydrocarbyl, R¹⁷ and R¹⁸ are independently hydrogen orlower hydrocarbyl provided that when there are two or more substituentsZ, they may be the same or different; and

m is 0 or an integer from 1 to 5.

The expression lower hydrocarbyl in the foregoing definitions, whetherthe expression is used on its own or as part of a larger radical such asfor example lower hydrocarbyloxy, is intended to include hydrocarbylradicals of, for example, up to ten carbon atoms. Subclasses of suchhydrocarbyl radicals include radicals with up to four, or up to sixcarbon atoms. The expression hydrocarbyl is intended to include withinits scope aliphatic, alicyclic, and aromatic hydrocarbyl groups andcombinations thereof. It thus includes, for example, alkyl, alkenyl, andalkynyl radicals, cyclopropyl, cyclopropylmethyl, cyclobutyl,cyclopentyl, and cyclohexyl radicals, the adamantyl radical and thephenyl radical.

When the lower hydrocarbyl group is substituted, the substituents mayinclude, for example, halogen (i.e. chlorine, bromine, fluorine oriodine), hydroxy, SO₂ NR^(a) R^(b) (where R^(a) and R^(b) areindependently H or C₁₋₆ alkyl), cyano, nitro, amino, mono- anddialkylamino in which the alkyl groups have from 1 to 6 or more carbonatoms, acylamino, C₁₋₆ alkoxy, C₁₋₆ haloalkoxy, C₁₋₆ alkylthio, C₁₋₆alkylsulphinyl, C₁₋₆ alkylsulphonyl, carboxy, carboxyamide in which thegroups attached to the N atom may be hydrogen or optionally substitutedlower hydrocarbyl; alkoxy carbonyl wherein the alkoxy group may havefrom 1 to 6 or more carbon atoms, and aryl such as phenyl.

The expression heteroaryl in the foregoing definitions is intended toinclude such radicals as pyridyl, pyrimidyl, triazinyl, thienyl, furyl,and thiazolyl. When the heteroaryl radical is substituted, thesubstituents may include those recited above for substituted lowerhydrocarbyl.

Particular examples of values for R¹ and R² include hydrogen, methyl,ethyl, propyl, iso-propyl, n-butyl, iso-butyl, sec-butyl, t-butyl,n-pentyl and its isomers such as C(CH₃)₂ CH₂ CH₃, n-hexyl and itsisomers, n-heptyl and its isomers, C(CH₃)₂ C.tbd.CH, C(CH₃)CH.tbd.CH₂,C(CH₃)₂ CN, alpha-methyl benzyl, cyclohexyl, cyclopentyl, cyclobutyl,cyclopropyl, 1-methyl cyclohexyl, 1-methyl-cyclopentyl,1-methyl-cyclobutyl, 1-methyl-cyclopropyl, 1-cyano-cyclohexyl,1-cyano-cyclopentyl, 1-cyano-cyclobutyl, 1-cyano-cyclopropyl,1-ethynyl-cyclohexyl, 1-ethynyl-cyclopentyl, 1-ethynyl-cyclobutyl,1-ethynyl-cycloypropyl, phenyl, p-chlorophenyl and benzyl. When R¹ andR² together with the nitrogen atom to which they are attached, form aheterocyclic ring, the ring may be for example a pyrrolidino,piperidino, thiomorpholino or morpholino ring, each of which may besubstituted, e.g. with one or more methyl groups.

Examples of particular values for Z include methyl, ethyl, n-propyl,iso-propyl, trifluoromethyl, difluoromethyl, pentafluoroethyl,trichloromethyl, ethoxyvinyl, fluorine, chlorine, bromine, iodine,methoxy, ethoxy, n-propoxy, iso-propoxy, trifluoromethoxy,tetrafluoroethoxy, cyano, nitro, amino, mono- or dialkylamino in whicheach alkyl group may have from 1 to 6 or more carbon atoms,hydroxylamino, acyl (e.g. acetyl or trifluoroacetyl), methylthio,methylsulphinyl, methylsulphonyl, trifluoromethylthio,trifluoromethylsulphinyl, trifluoromethylsulphonyl, sulphonamido,carboxy, alkoxycarbonyl in which the alkoxy group may have from 1 to 6or more carbon atoms, carboxyamide in which the groups attached to the Natom may be hydrogen or optionally substituted lower hydrocarbyl; oracylamino (e.g. acetamido). When there is more than one substituent Z,the substituents may be the same or different.

Preferred values for Z are CF₃, OCF₃, OCHF₂, CHF₂, OMe, F, Cl, Br, I,NH₂, NO₂, CN, C₁₋₄ alkyl, C₁₋₄ alkoxy, COC₁₋₄ alkyl, NHCDC₁₋₄ alkyl, SO₂C₁₋₄ alkyl, OCF₂ CHF₂, CF₂ CF₃, OCF₂ CHF₂ and SO₂ NR⁸ R⁹.

Especially preferred values for Z are CF₃, OCF₃, OCH₃, F, Cl, Br and I.

m is preferably 1, 2 or 3.

The preferred substitution pattern for the Z groups is for a single Zgroup at the 3-position; or two Z groups at the 3,4- and 3,5- positions;or three Z groups at the 3, 4 and 5 positions, the Z group at the4-position being halo, especially fluoro.

R¹ is preferably iso-propyl, sec-butyl, t-butyl, C(CH₃)₂ C.tbd.CH,C(CH₃)₂ CH═CH₂, C(CH₃)₂ CH₂ CH₃ or a 3-6 membered cyloalkyl, optionallysubstituted by CH₃ or C.tbd.CH at the α position of the cycloalkyl ring.

R² is preferably hydrogen or C₁₋₄ alkyl, especially hydrogen.

Preferably R³, R⁴, R⁵ and R⁶ are hydrogen.

The formula (I) given above is intended to include tautomeric forms ofthe structure drawn, as well as physically distinguishable modificationsof the compounds which may arise, for example, from different ways inwhich the molecules are arranged in a crystal lattice, or from theinability of parts of the molecule to rotate freely in relation to otherparts, or from geometrical isomerism, or from intra-molecular orinter-molecular hydrogen bonding, or otherwise.

Compounds of the invention exist in enantiomeric or diastereomericforms. The invention includes all individual forms and mixtures thereofin all proportions.

Particular examples of compounds of the invention are listed in Table I.

                  TABLE I                                                         ______________________________________                                        Compound                                                                      No      Z(m)      R.sup.1 R.sup.2                                                                             R.sup.3                                                                           R.sup.4                                                                             R.sup.5                                                                           R.sup.6                         ______________________________________                                        1       3-CF.sub.3                                                                              C(Me).sub.3                                                                           H     H   H     H   H                               ______________________________________                                    

Compounds of formula {I}are suitably prepared by a variety of processes.

In particular compounds of formula (I) can be prepared by reacting acompound of formula (II) where R¹, R², R³, R⁴, R⁵ and R⁶ Z and m are asdefined in relation to formula (I): with Lawessons Reagent (formula III)in a solvent such as toluene at 80° to 115° C. in the presence of abase. Suitable bases include weak bases such as triethylamine, pyridineor N-ethyl-N,N-diisopropyl amine.

Compounds of formula (II) can be prepared by reacting a compound offormula (IV) where R³, R⁴, R⁵, R⁶, Z and m are as defined in relation toformula (I): with a compound of formula (V) or, where R² is hydrogen, acompound of formula (VI) where R¹ is as defined in relation to formula(I) and R¹⁹ is a leaving group in the presence of a base.

Suitable bases include weak bases such as triethylamine, pyridine orN-ethyl-N,N-diisopropyl amine.

Suitable leaving groups R¹⁹ include halogen such as chloro.

The reaction is suitably effected in an organic solvent such asdichloromethane, trichloromethane, tetrahydrofuran or diethyl ether attemperatures of from 0° to 80° C., preferably at ambient temperature.

An alternative method of preparing compounds of formula from compoundsof formula (IV) is by reacting the compound of formula (IV) withClC(O)OCH(Cl)CCl₃ in the presence of a base to product a compound offormula (XIII) in which R³, R⁴, R⁵, R⁶, Z and m are as defined inrelation to formula (I). The reaction is suitably carried out at from-10° to 10° C. in the presence of a solvent. Suitable bases areheteroaromatic nitrogen bases, such as pyridine. Suitable solvents aredichloromethane or chloroform. The compounds of formula (XIII) are thenreacted with an amine of formula (VIII) HNR¹ R² where R¹ and R² are asdefined in relation to formula (I) to produce a compound of formula (I).The reaction is suitably carried out at from -10° to 30° C. in thepresence of a base, and a solvent. Suitable bases are pyridine, andtriethylamine. Suitable solvents are dichloromethane or chloroform. Thecompounds of formula (XIII) need not be isolated, but can be reacted insitu with the compound of formula (VIII).

Instead of ClC(O)OCH(Cl)CCl₃ the compounds of formula (IV) as definedabove may be reacted with phosgene to produce a compound of formula(XIV) in which R³, R⁴, R⁵, R⁶ Z, and m are as defined in relation toformula (I). The compounds of formula (XIV) are then reacted with amineof formula (VIII) as hereinbefore defined to produce a compound offormula (I). The reaction is suitably carried out at from -20° to 50° C.in the presence of a base and a solvent.

Suitable bases are pyridine or triethylamine. Suitable solvents arechloroform, dichloro methane or tetrahydrofuran. The compound of formula(XIV) need not be isolated and can be reacted in situ with the compoundof formula (VIII).

Alternatively compounds of formula (IV) may be produced by hydrolysis ofa compound of formula (VII): where R³, R⁴, R⁵, R⁶, Z and m are asdefined in relation to formula (I) and R²⁰ is OCOR²¹. The reaction isconveniently carried out in the presence of an alcohol, such asmethanol, and silica gel.

Suitably group R²¹ is trifluoromethyl. The reaction is suitably effectedin a solvent such as dichloromethane at temperatures of from 0° to 50°C., preferably ambient temperature.

Compounds of formula (IV) may be also be prepared by oxygenating acompound of formula (X), where R³, R⁴, R⁵, R⁶, Z and m are as defined inrelationship to formula (I), with a strong base such as LiN(SiMe₃)₂ orLiN(iPr)₂, followed by reaction with a compound of formula (XVII).

The reaction is suitably effected in a solvent such as tetrahydrofuranat temperatures of from -100° to 30° C., preferably from -80° to 0° C.In compounds of formula (XVII) Ar is suitably a p-tolyl group and Ar' issuitably phenyl.

Where the substituents Z are of a nature and distribution to activatethe phenyl ring to nucleophilic substitution it is possible to couple acompound of formula (XI); where Z and m are as defined and R²² is aleaving group, with a compound of formula (XII); where R³, R⁴, R⁵, andR⁶, are as defined in relationship to formula (I), in the presence of abase.

Suitable leaving groups R²² include halogen such as fluoro.

Suitable bases include strong bases such as potassium hydroxide orsodium hydroxide.

The reaction is suitably effected in an organic solvent such asdimethylsulphoxide or dimethylformamide at temperatures of from 0° to90° C.

Examples of suitable compounds of formula (XI) include3,4-difluoro-5-chloro-α,α,α-trifluorotoluene and3,4,5-trifluoro-α,α,α-trifluorotoluene.

Compounds of formula (X) where R³, R⁴, R⁵ and R⁶ are hydrogen and Z andm are as defined in relationship to formula (I), may be prepared byheating and decarboxylating a compound of formula (XX) were R³, R⁴, R⁵and R⁶ are hydrogen and Z and m are as defined in relationship toformula (I). Compounds of formula (XX) may be produced by reacting acompound of formula (XVIV) where Z and m are as defined in relationshipto formula (I), with a compound of formula (XXI) prepared according tothe method described in Organic Syntheses Vol 60 p66-68.

Compounds of formula (V), (VI), (VIII), (XI), (XII) and (XIV) are knowncompounds or may be prepared from known compounds by known methods.

Variations of the above procedures will be apparent to the skilledperson in the art, as well as alternative processes for preparing thecompounds of the invention.

The compounds of formula (I) above are active as herbicides, and theinvention therefore provides in a further aspect a process for severelydamaging or killing unwanted plants, which process comprises applying tothe plants, or to the growth medium of the plants, a herbicidallyeffective amount of a compound of formula (I) as hereinbefore defined.

The compounds of formula (I) are active against a broad range of weedspecies including monocotyledonous and dicotyledonous species. They showsome selectivity towards certain species; they may be used, for example,as selective herbicides in soya and maize crops. The compounds offormula (I) are applied directly to unwanted plants (post-emergenceapplication) but they are preferably applied to the soil before theunwanted plants emerge (pre-emergence application).

The compounds of formula (I) may be used on their own to kill orseverely damage plants, but are preferably used in the form of acomposition comprising a compound of formula (I) in admixture with acarrier comprising a solid or liquid diluent.

Compositions containing compounds of formula (I) include both dilutecompositions, which are ready for immediate use, and concentratedcompositions, which require to be diluted before use, usually withwater. Preferably the compositions contain from 0.01% to 90% by weightof the active ingredient. Dilute compositions ready for use preferablycontain from 0.01 to 2% of active ingredient, while concentratedcompositions may contain from 20 to 90% of active ingredient, althoughfrom 20 to 70% is usually preferred.

The solid compositions may be in the form of granules, or dustingpowders wherein the active ingredient is mixed with a finely dividedsolid diluent, e.g. kaolin, bentonite, kieselguhr, dolomite, calciumcarbonate, talc, powdered magnesia, Fuller's earth and gypsum. They mayalso be in the form of dispersible powders or grains, comprising awetting agent to facilitate the dispersion of the powder or grains inliquid. Solid compositions in the form of a powder may be applied asfoliar dusts.

Liquid compositions may comprise a solution or dispersion of an activeingredient in water optionally containing a surface-active agent, or maycomprise a solution or dispersion of an active ingredient in awater-immiscible organic solvent which is dispersed as droplets inwater.

Surface-active agents may be of the cationic, artionic, or non-ionictype or mixtures thereof. The cationic agents are, for example,quaternary ammonium compounds (e.g. cetyltrimethylammonium bromide).Suitable anionic agents are soaps; salts of aliphatic mono ester ofsulphuric acid, for example sodium lauryl sulphate; and salts ofsulphonated aromatic compounds, for example sodiumdodecylbenzenesulphonate, sodium, calcium, and ammonium lignosulphonate,butylnaphthalene sulphonate, and a mixture of the sodium salts ofdiisopropyl and triisopropylnaphthalenesulphonic acid. Suitablenon-ionic agents are the condensation products of ethylene oxide withfatty alcohols such as oleyl alcohol and cetyl alcohol, or withalkylphenols such as octyl- or nonyl- phenol (e.g. Agral 90) oroctyl-cresol. Other non-ionic agents are the partial esters derived fromlong chain fatty acids and hexitol arthydrides, for example sorbitanmonolaurate; the condensation products of the partial ester withethylene oxide; the lecithins; and silicone surface active agents (watersoluble surface active agents having a skeleton which comprises asiloxane chain e.g. Silwet L77). A suitable mixture in mineral oil isAtplus 411F.

The aqueous solutions or dispersions may be prepared by dissolving theactive ingredient in water or an organic solvent optionally containingwetting or dispersing agent(s) and then, when organic solvents are used,adding the mixture so obtained to water optionally containing wetting ordispersing agent(s). Suitable organic solvents include, for example,ethylene di-chloride, isopropyl alcohol, propylene glycol, diacetonealcohol, toluene, kerosene, methylnaphthalene, the xylenes andtrichloroethylene.

The compositions for use in the form of aqueous solutions or dispersionsare generally supplied in the form of a concentrate containing a highproportion of the active ingredient, and the concentrate is then dilutedwith water before use. The concentrates are usually required towithstand storage for prolonged periods and after such storage, to becapable of dilution with water to form aqueous preparations which remainhomogeneous for a sufficient time to enable them to be applied byconventional spray equipment. Concentrates conveniently contain 20-90%,preferably 20-70%, by weight of the active ingredient(s). Dilutepreparations ready for use may contain varying amounts of the activeingredient(s) depending upon the intended purpose; amounts of 0.01% to10.0% and preferably 0.14 to 2%, by weight of active ingredient(s) arenormally used.

A preferred form of concentrated composition comprises the activeingredient which has been finely divided and which has been dispersed inwater in the presence of a surface-active agent and a suspending agent.Suitable suspending agents are hydrophilic colloids and include, forexample, polyvinylpyrrolidone and sodium carboxymethylcellulose, and thevegetable gums, for example gum acacia and gum tragacanth. Preferredsuspending agents are those which impart thixotropic properties to, andincrease the viscosity of the concentrate. Examples of preferredsuspending agents include hydrated colloidal mineral silicates, such asmontmorillonite, beidellite, nontronite, hectorite, saponite, andsaucorite. Bentonite is especially preferred. Other suspending agentsinclude cellulose derivatives and polyvinyl alcohol.

The rate of application of the compounds of the invention will depend ona number of factors including, for example, the compound chosen for use,the identity of the plants whose growth is to be inhibited, theformulations selected for use and whether the compound is to be appliedfor foliage or root uptake. As a general guide, however, an applicationrate of from 0.001 to 20 kilograms per hectare is suitable while from0.025 to 10 kilograms per hectare may be preferred.

The compositions of the invention may comprise, in addition to one ormore compounds of the invention, one or more compounds not of theinvention but which possess biological activity. Accordingly in yet astill further embodiment the invention provides a herbicidal compositioncomprising a mixture of at least one herbicidal compound of formula (I)as hereinbefore defined with at least one other herbicide.

The other herbicide may be any herbicide not having the formula (I). Itwill generally be a herbicide having a complementary action in theparticular application.

Examples of useful complementary herbicides include:

A. benzo-2,1,3-thiadiazin-4-one-2,2-dioxides such as bentazone;

B. hormone herbicides, particularly the phenoxy alkanoic acids such asMCPA, MCPA-thioethyl, dichlorprop, 2,4,5-T, MCPB, 2,4-D, 2,4-DB,mecoprop, trichlopyr, clopyralid, and their derivatives (eg. salts,esters and amides);

C. 1,3 dimethylpyrazole derivatives such as pyrazoxyfen, pyrazolate andbenzofenap;

D. Dinitrophenols and their derivatives (eg. acetates) such as dinoterb,dinoseb and its ester, dinoseb acetate;

E. dinitroaniline herbicides such as dinitramine, trifluralin,ethalflurolin, pendimethalin, oryzalin;

F. arylurea herbicides such as diuron, flumeturon, metoxuron, neburon,isoproturon, chlorotoluron, chloroxuron, linuron, monolinuron,chlorobromuron, daimuron, methabenzthiazuron;

G. phenylcarbamoyloxyphenylcarbamates such as phenmedipham anddesmedipham;

H. 2-phenylpyridazin-3-ones such as chloridazon and norflurazon;

I. uracil herbicides such as lenacil, bromacil and terbacil;

J. triazine herbicides such as atrazine, simazine, aziprotryne,cyanazine, prometryn, dimethametryn, simetryne, and terbutryn;

K. phosphorothioate herbicides such as piperophos, bensulide, andbutamifos;

L. thiolcarbamate herbicides such as cycloate, vernolate, molinate,thiobencarb, butylate* , EPTC* , tri-allate, di-allate, esprocarb,tiocarbazil, pyridate, and dimepiperate;

M. 1,2,4-triazin-5-one herbicides such as metamitron and metribuzin;

N. benzoic acid herbicides such as 2,3,6-TBA, dicamba and chloramben;

O. anilide herbicides such as pretilachlor, butachlor, alachlor,propachlor, propanil, metazachlor, metolachlor, acetochlor, anddimethachlor;

P. dihalobenzonitrile herbicides such as dichlobenil, bromoxynil andioxynil;

Q. haloalkanoic herbicides such as dalapon, TCA and salts thereof;

R. diphenylether herbicides such as lactofen, fluroglycofen or salts orester thereof, nitrofen, bifenox, aciflurofen and salts and estersthereof, oxyfluorfen, fomesafen, chlornitrofen and chlomethoxyfen;

S. phenoxyphenoxypropionate herbicides such as diclofop and estersthereof such as the methyl ester, fluazifop and esters thereof,haloxyfop and esters thereof, quizalofop and esters thereof andfenoxaprop and esters thereof such as the ethyl ester;

T. cyclohexanedione herbicides such as alloxydim and salts thereof,sethoxydim, cycloxydim, tralkoxydim, and clethodim;

U. sulfonyl urea herbicides such as chlorosulfuron, sulfometuron,metsulfuron and esters thereof; benzsulfuron and esters thereof such asDPX-M6313, chlorimuron and esters such as the ethyl ester thereofpirimisulfuron and esters such as the methyl ester thereof, 2-3-(4-methoxy-6-methyl-1,3,5-triazin-zyl)-3-methylureidosulphonyl)benzoic acid esters such as the methyl ester thereof (DPX-LS300) andpyrazosulfuron;

V. imidazolidinone herbicides such as imazaquin, imazamethabenz,imazapyr and isopropylammonium salts thereof, imazethapyr;

W. arylanilide herbicides such as flamprop and esters thereof,benzoylprop-ethyl, diflufenican;

X. amino acid herbicides such as glyphosate and glufosinate and theirsalts and esters, sulphosate and bialaphos;

Y. organoarsenical herbicides such as monosodium methanearsonate (MSMA);

Z. herbicidal amide derivative such as napropamide, propyzamide,carbetamide, tebutam, bromobutide, isoxaben, naproanilide and naptalam;

AA. miscellaneous herbicides including ethofumesate, cinmethylin,difenzoquat and salts thereof such as the methyl sulphate salt,clomazone, oxadiazon, bromofenoxim, barban, tridiphane, flurochloridone,quinchlorac, mefanacet, and triketone herbicides such as sulcotrione;

BB. Examples of useful contact herbicides include: bipyridyliumherbicides such as those in which the active entity is paraquat andthose in which the active entity is diquat;

* These compounds are preferably employed in combination with a safenersuch as dichlormid.

The invention is illustrated by the following Examples. (The preparationof intermediates is described in the Preparative Examples). Theabbreviations used in the Examples have the following meanings:

NMR spectrum: nuclear magnetic resonance spectrum which were recorded at270 or 400 MHz. (This refers to the proton magnetic resonance spectrumunless otherwise stated). The following abbreviations are used toindicate the multiplicity of the peaks in the NMR spectrum: s (singlet);d (doublet); t (triplet); q (quartet) quin (quintet) m (multiplet; br(broad).

IR spectrum: infra-red absorption spectrum.

MS: mass spectrum

GC: gas chromatography TLC: thin layer chromatography

m.p.: melting point b.p: boiling point

EXAMPLE 1 Preparation of3-t-Butylcarbamoyloxy-1-(3-trifluoromethyl)phenyl-pyrrolidine-2-thione(Compound No. 1)

3-t-Butylcarbamoyloxy-1-(3-trifluoromethyl)phenyl-2-pyrrolidinone (0.25g) was dissolved in toluene (25 ml) and stirred under nitrogen at roomtemperature. To this solution was added diisopropylethylamine (0.479 g)and Lawesson's Reagent(2,4-bis(4-methoxyphenyl)-1,3-dithia-2,4-diphosphetane-2,4-disulphide)(1.47 g), and the reaction mixture heated to 80-90° C. for 80 minutes.The reaction mixture was then allowed to cool to room temperature andevaporated to dryness under reduced pressure. The residue was purifiedby silica gel chromatography (20-30% ethyl acetate-hexane as eluant) togive a solid which was further purified by recrystallisation from ethylacetate-hexane. The title compound was obtained as a white solid, yield0.169 g, m.p. 151.5°-152.5° C. ¹ H NMR (CDCl₃): δ1.36 (9H, s); 2.21 (1H,m); 2.79 (1H, m); 4.09 (2H, m); 4.92 (1H, broad s); 5.59 (1H, t); 7.59(2H, m); 7.84 (2H, m). MS: m/e 360 (M⁺).

Preparative Example 1. Preparation of3-hydroxy-1-(3-trifluoromethyl)phenyl-2-pyrrolidinone

Step 1 Preparation of1-(3-trifluoromethyl)phenyl-2-pyrrolidinone-3-carboxylic acid

A suspension of 6,6-dimethyl-5,7-dioxaspiro 2,5!octane-4,8-dione(prepared as described in Organic Syntheses, Volume 60, p66-68) (8.00 g)in 3-trifluoromethylaniline (8.05 g) was stirred at room temperature for24 hours. The mixture was filtered, and the insoluble solid was washedwith chloroform. The combined filtrates were washed with 2M hydrochloricacid, brine and then dried (MgSO₄). Evaporation of the solvent underreduced pressure left a brown solid, which was recrystallised fromchloroform/hexane to give the product as a white, crystalline solid,yield 4.10 g, mp 135°-136° C. (dec).

¹ H nmr (CDCl₃): δ2.47-2.67 (2H, m), 3.70 (1H, t), 3.92-4.01 (2H, m),7.00 (broad), 7.45-7.60 (2H, m), 7.81-7.90 (2H, m)

Step 2 Preparation of 1-(3-trifluoromethyl)phenyl-2-pyrrolidinone

1-(3-trifluoromethyl)phenyl-2-pyrrolidinone-3-carboxylic acid (preparedas in Step 1 above) (3.60 g) was heated to its melting point, andheating was continued until effervescence ceased (ca 50 minutes). Themelt was cooled, dissolved in diethyl ether, and treated withdecolourising charcoal. The charcoal was filtered off, and the solventwas removed under reduced pressure to leave a solid residue. This wasrecrystallised from hexane to give the product as colourless needles,yield 2.209, mp 67°-68° C.

¹ H nmr (CDCl₃): 67.19 (2H, quin), 2.62 (2H, t), 3.89 (2H, t), 7.35-7.53(2H, m), 7.81-7.93 (2H, m)

MS: m/e 229 (M⁺)

Step 3 Preparation of3-hydroxy-1-(3-trifluoromethyl)phenyl-2-pyrrolidinone

A stirred solution of 1-(3-trifluoromethyl)phenyl-2-pyrrolidinone(prepared as in Step 2 above) (1.10 g) in dry tetrahydrofuran (5 ml) wascooled to -70° C. under a nitrogen atmosphere, and a solution of lithiumhexamethyldisilazide in hexanes (1.0M, 4.9 ml) was added dropwise. Theresultant pale yellow suspension was then treated with a solution ofN-toluenesulphonyl-3-phenyloxaziridine (prepared as described in Journalof Organic Chemistry, 1988, 53, 2087) (2.00 g) in dry tetrahydrofuran (5ml). The resultant pale yellow solution was allowed to warm to roomtemperature, and was then quenched with water and acidified to pH5 using2M hydrochloric acid. The mixture was extracted with diethyl ether (×2),and the combined extracts were washed with water, dried (MgSO₄) andevaporated under reduced pressure to leave an oil. Purification bysilica gel chromatography, eluting with ethyl acetate/hexane mixtures,afforded the title compound as a clear gum, yield 0.26 g.

¹ H nmr (CDCl₃): δ1.62 (1H, broad s), 2.12 (1H, m), 2.63 (1H, m),3.72-3.90 (2H, m), 4.51 (1H, m), 7.39-7.58 (2H, m), 7.77-8.02 (2H, m)

MS: m/e 245 (M⁺)

Step 4 3-t-butylcarbamoyloxy-1-(3-trifluoromethyl)phenyl-2-pyrrolidinone

A stirred solution of3-hydroxy-1-(3-trifluoromethyl)phenyl-2-pyrrolidinone (prepared as inStep 3 above) (0.220 g) in dichloromethane (2 ml) was treated withtert-butyl isocyanate (0.063 g) followed by triethylamine (0.084 ml).The solution was stirred for 24 hours, then evaporated under reducedpressure. Purification of the residue by silica gel chromatography,eluting with ethyl acetate/hexane mixtures, afforded the title compoundas a clear gum, yield 0.060 g.

¹ H nmr (CDCl₃): δ1.35 (9H, s), 2.13 (1H, m), 2.73 (1H, m), 3.80-3.89(2H, m), 4.94 (1H, broad s), 5.38 (1H, t), 7.38-7.53 (2H, m), 7.89-7.95(2H, m)

Biological Data

The herbicidal activity of the compounds was tested as follows: Eachchemical was formulated in one of two ways. Either the chemical wasdissolved in an appropriate amount of water, dependent on the amount ofsolvent/surfactant blend required such that the total volume is 5 cm³.Then a solvent sufficient blend comprised 78.2 gm/liter of Tween 20 and21.8 gm/liter of Span 80 adjusted to 1 liter using methylcyclohexanonewas added to the solution. Alternatively, the chemical was dissolved inwater to the required concentration and 0.1% Tween added. Tween 20 is aTrade Mark for a surface-active agent comprising a condensate of 20molar proportions of ethylene oxide with sorbitan laurate. Span 80 is aTrade Mark for a surface-active agent comprising sorbitan mono-laurate.If the chemical did not dissolve, the volume was made up to 5 cm³ withwater, glass beads were added and this mixture was then shaken to effectdissolution or suspension of the chemical, after which the beads wereremoved. In all cases, the mixture was then diluted to the requiredspray volume. If sprayed independently, volumes of 25 cm³ and 30 cm³were required for post-emergence tests; if sprayed together, 45 cm³ wasrequired. The sprayed aqueous emulsion contained 4% of the initialsolvent/surfactant mix and the test chemical at an appropriateconcentration.

The spray compositions so prepared were sprayed on to young pot plants(post-emergence test) at a spray volume equivalent to 1000 liters perhectare. Damage to plants was assessed 13 days after spraying bycomparison with untreated plants, on a scale of 0 to 9 where 0 is 0%damage, 1 is 1-5% damage, 2 is 6-15% damage, 3 is 16-25% damage, 4 is26-35% damage, 5 is 36-59% damage, 6 is 60-69% damage, 7 is 70-79%damage, 8 is 80-89% damage and 9 is 90-100% damage.

In a test carried out to detect pre-emergence herbicidal activity, cropseeds were sown at 2 cm depth and weed seeds at 1 cm depth beneathcompost and sprayed with the compositions at the rate of 1000 liters perhectare. 20 days after spraying, the seedlings in the sprayed plastictrays were compared with the seedlings in unsprayed control trays, thedamage being assessed on the same scale of 0 to 9. ##STR2##

We claim:
 1. A compound of formula (I):Wherein R¹ and R² are eachindependently hydrogen, optionally substituted lower hydrocarbyl, oroptionally substituted heteroaryl, or R¹ and R² together with thenitrogen atom to which they are attached, form a heterocyclic ring; R³,R⁴, R⁵ and R⁶ are independently H or C₁₋₄ alkyl; Z represents halogen,optionally substituted lower hydrocarbyl, optionally substituted lowerhydrocarbyloxy, optionally substituted lower hydrocarbylthio,hydrocarbylsulphinyl, or hydrocarbylsulphonyl, cyano, nitro, CHO, NHOH,ONR^(7') R^(7"), SF₅, CO(optionally substituted lower hydrocarbyl),acylamino, COOR⁷, SO₂ NR⁸ R⁹, CONR¹⁰ R¹¹, OR¹² or NR¹³ R¹⁴ where R⁷,R^(7'), R^(7"), R⁸, R⁹, R¹⁰ and R¹¹ are independently H or lowerhydrocarbyl; R¹² is hydrogen, SO₂ lower hydrocarbyl or COR¹⁵ ; R¹³ andR¹⁴ are independently lower hydrocarbyl, lower hydrocarbyloxy or a groupR¹² ; R¹⁵ is OR¹⁶, NR¹⁷ R¹⁸, hydrogen or lower hydrocarbyl; R¹⁶ is lowerhydrocarbyl, R¹⁷ and R¹⁸ are independently hydrogen or lower hydrocarbylprovided that when there are two or more substituents Z, they may be thesame or different; and m is 0 or an integer from 1 to
 5. 2. A process ofseverely damaging or killing unwanted plants, which comprises applyingto the plants, or to the growth medium of the plants, a herbicidallyeffective amount of a compound of formula (I) as defined in claim
 1. 3.A herbicidal composition comprising a compound of formula (I) as definedin claim 1 in combination with a herbicidal carrier or diluent.
 4. Acompound of formula (I) as defined in claim 1, wherein Z representsmethyl, ethyl, n-propyl, iso-propyl, trifluoromethyl, difluoromethyl,pentafluoroethyl, trichloromethyl, ethoxyvinyl, fluorine, chlorine,bromine, iodine, methoxy, ethoxy, n-propoxy, iso-propoxy,trifluoromethoxy, tetrafluoroethoxy, cyano, nitro, amino, mono- ordialkylamino in which each alkyl group may have from 1 to 6 carbonatoms, hydroxylamino, acyl, methylthio, methylsulphinyl,methylsulphonyl, trifluoromethylthio, trifluoromethylsulphinyl,trifluoromethylsulphonyl, sulphonamido, carboxy, alkoxycarbonyl in whichthe alkoxy group may have from 1 to 6 carbon atoms, carboxyamide inwhich the groups attached to the N atom may be hydrogen or optionallysubstituted lower hydrocarbyl or acylamino; provided that when there aretwo or more substituents Z, they may be the same or different.
 5. Acompound of formula (I) as defined in claim 4, wherein Z represents CF₃,OCF₃, OCHF₂, CHF₂, OMe, F, Cl, Br, I, NH₂, NO₂, CN, C₁₋₄ alkyl, C₁₋₄alkoxy, COC₁₋₄ alkyl, NHCOC₁₋₄ alkyl, SO₂ C₁₋₄ alkyl, OCF₂ CHF₂, CF₂CF₃, OCF₂ CHF₂ or SO₂ NR⁸ R⁹, provided that when there are two or moresubstituents Z, they may be the same or different.
 6. A compound offormula (I) as defined in claim 1, wherein m represents 1, 2 or
 3. 7. Acompound of formula (I) as defined in claim 1, wherein R¹ representsiso-propyl, sec-butyl, t-butyl, C(CH₃)₂ C.tbd.CH, C(CH₃)₂ CH.tbd.CH₂,C(CH₃)₂ CH₂ CH₃ or a 3-6 membered cycloalkyl ring, optionallysubstituted by CH₃ or C.tbd.CH at the α position of the cycloalkyl ring.8. A compound of formula (I) as defined in claim 1, wherein R² ishydrogen or C₁₋₄ alkyl.
 9. A compound of formula (I) as defined in claim1, wherein R³, R⁴, R⁵ and R⁶ are hydrogen.